Force-sensing modules for light sensitive screens

ABSTRACT

A light sensitive screen includes at least one sensing element each being configured to detect a force applied to a position of the light sensitive screen and generate an electrical signal when a force is detected, and a sensor module configured to receive and process the electrical signal from the at least one sensing element. The sensor module may amplify the electrical signal from one of the at least one sensing element and generate an amplified signal, compare the amplified signal with a threshold and generate a comparing result, and generate a digital signal based on the comparing result, the digital signal including information as to whether the position of the light sensitive screen is touched.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 12/403,415filed Mar. 13, 2009, the entirety of which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to touch panels. More particularly, thepresent invention relates to force-sensing modules for light sensitivescreens.

2. Description of the Prior Art

Touch panels or touch screens capable of providing user interface anduser interaction have been widely used in electronic products such aspersonal computers, cellular phones, personal digital assistants and thelike. In operation, it may be necessary for a touch panel to detect atouched position thereon. To detect whether a position is touched, aconventional method called “Carroll method” disclosed in U.S. Pat. No.4,267,443 to Carroll et al. may be generally employed. In the Carrollmethod, an optical matrix comprising a plurality of light emittingelements such as LEDs and a matrix of light receiving elements maybearranged on a front surface of a screen. A position at the front surfaceof the screen where a light beam emitted from a light emitting elementmay be blocked by the touch of a pen or finger may be detected by thelight receiving elements.

Some conventional touch panels or light sensitive screens may detect achange in brightness at a position of the panel due to an approaching orleaving force source and, based on the brightness change, identifywhether the position is pressed or touched. For example, an approachingfinger or pen may cast a shadow over the position and cause a change inbrightness. However, it may be difficult to distinguish a “real” touchthat the finger or pen is actually pressed on the position from a“quasi” touch that the approaching finger or pen, though cause asignificant brightness change for being very close to the position, doesnot physically touch or contact the position. A misunderstanding of thetouch status may result in malfunction of the panels or undesiredoperation on the panels.

SUMMARY OF THE INVENTION

Examples of the present invention may provide a light sensitive screencomprising at least one sensing element each being configured to detecta force applied to a position of the light sensitive screen and generatean electrical signal when a force is detected, the electrical signalincluding a positive half and a negative half, and a sensor moduleconfigured to receive and process the electrical signal from the atleast one sensing element, the sensor module comprising an amplifierconfigured to amplify the electrical signal from one of the at least onesensing element and generate an amplified signal, a comparatorconfigured to compare one of the positive half and the negative halfwith a threshold and generate a first voltage signal and a secondvoltage signal, the first voltage signal and the second voltage havingthe same amplitude with different signs, and a digitizer configured togenerate a digital signal based on the first voltage signal and thesecond voltage signal, the digital signal including information as towhether the position of the light sensitive screen is touched.

Some examples of the present invention may provide a light sensitivescreen comprising at least one sensing element each being configured todetect a force applied to a position of the light sensitive screen andgenerate an electrical signal when a force is detected, and a sensormodule configured to receive and process the electrical signal from theat least one sensing element, the sensor module comprising an amplifierconfigured to amplify the electrical signal from one of the at least onesensing element and generate an amplified signal, a rectifier configuredto convert the amplified signal into a direct-current (DC) signalincluding a first positive half and a second positive half, a triggerconfigured to detect an edge each of the first positive half and thesecond positive half, and generate a first pulse signal and a secondpulse signal for the first positive half and the second positive half,respectively, and a digitizer configured to generate a digital signalbased on the first pulse signal and the second pulse signal, the digitalsignal including information as to whether the position of the lightsensitive screen is touched.

Examples of the present invention may further provide a light sensitivescreen comprising at least one sensing element each being configured todetect a force applied to a position of the light sensitive screen andgenerate an electrical signal when a force is detected, the electricalsignal including a positive half and a negative half, and a sensormodule configured to receive and process the electrical signal from theat least one sensing element, the sensor module comprising an amplifierconfigured to amplify the electrical signal from one of the at least onesensing element and generate an amplified signal, an integrator tointegrate the amplified signal from the amplifier and generate anintegrated signal, a comparator configured to compare the integratedsignal with a threshold, and a digitizer configured to generate adigital signal based on a result of comparison from the comparator, thedigital signal including information as to whether the position of thelight sensitive screen is touched.

Examples of the present invention may also provide a light sensitivescreen comprising at least one sensing element each being configured todetect a force applied to a position of the light sensitive screen andgenerate an electrical signal when a force is detected, and a sensormodule configured to receive and process the electrical signal from theat least one sensing element, the sensor module comprising an amplifierconfigured to amplify the electrical signal from one of the at least onesensing element and generate an amplified signal, a rectifier configuredto convert the amplified signal into a direct-current (DC) signalincluding a first positive half and a second positive half, a peakdetector configured to detect a first peak value of the first positivehalf and a second peak value of the second positive half, and adigitizer configured to generate a digital signal based on the firstpeak value and the second peak value, the digital signal includinginformation as to whether the position of the light sensitive screen istouched.

Additional features and advantages of the present invention will be setforth in part in the description which follows, and in part will beobvious from the description, or may be learned by practice of theinvention. The features and advantages of the invention will be realizedand attained by means of the elements and combinations particularlypointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings examples which are presently preferred.It should be understood, however, that the invention is not limited tothe precise arrangements and instrumentalities shown.

In the drawings:

FIG. 1 is a schematic diagram illustrating an exemplary light sensitivescreen in operation;

FIG. 2A is a block diagram illustrating a force sensor module accordingto an example of the present invention;

FIG. 2B is a circuit diagram illustrating a force sensor moduleaccording to another example of the present invention;

FIG. 3A is a waveform diagram illustrating exemplary waveforms of aninput force and an amplified electrical signal;

FIG. 3B is a waveform diagram illustrating an exemplary waveform of arectified signal from a rectifier illustrated in FIG. 2B;

FIG. 3C is a diagram illustrating exemplary pulses from a triggerillustrated in FIG. 2B;

FIG. 3D is a waveform diagram illustrating an exemplary waveform of anoutput from a digitizer illustrated in FIG. 2B;

FIG. 4A is a block diagram illustrating a force sensor module accordingto yet another example of the present invention;

FIG. 4B is a circuit diagram illustrating a force sensor moduleaccording to still another example of the present invention;

FIG. 5A is a waveform diagram illustrating an exemplary waveform of anoutput from an integrator illustrated in FIG. 4B;

FIG. 5B is a waveform diagram illustrating an exemplary waveform of anoutput from a digitizer illustrated in FIG. 4B;

FIG. 6A is a block diagram illustrating a force sensor module accordingto yet still another example of the present invention;

FIG. 6B is a circuit diagram illustrating a force sensor moduleaccording to yet another example of the present invention;

FIG. 7A is a diagram illustrating exemplary peak signals from a peakdetector illustrated in FIG. 6B;

FIG. 7B is a waveform diagram illustrating an exemplary waveform of anoutput from a digitizer illustrated in FIG. 6B;

FIG. 8A is a block diagram illustrating a force sensor module accordingto still another example of the present invention;

FIG. 8B is a circuit diagram illustrating a force sensor moduleaccording to yet another example of the present invention;

FIG. 9A is a waveform diagram illustrating exemplary waveforms of aninput force and an amplified electrical signal;

FIGS. 9B and 9C are waveform diagrams illustrating exemplary waveformsof output voltages of a comparator illustrated in FIG. 8B; and

FIG. 9D is a waveform diagram illustrating an exemplary waveform of anoutput of a digitizer illustrated in FIG. 8B.

DETAILED DESCRIPTION

Reference will now be made in detail to the present examples of theinvention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a schematic diagram illustrating an exemplary light sensitivescreen 10 in operation. Referring to FIG. 1, the light sensitive screenor touch panel 10 may include a sensing element 12. In one example, thesensing element 12 may include one of a piezoelectric element based onthe piezoelectric effect and a piezoresistive element based on thepiezoresistive effect. The piezoelectric effect may refer to the abilityof piezoelectric materials, such as crystals and certain ceramics, togenerate an electric potential in response to applied mechanical stress.The piezoresistive effect, however, may cause a change in electricalresistance due to applied mechanical stress. Accordingly, the sensingelement 12 may generate an electrical signal when an applied force isdetected.

In operation, as a force source 14 such as a finger or a pen-like objecttouches a surface of the light sensitive screen 10, force from the forcesource 14 may cause mechanical stress on the light sensitive screen 10and in turn the sensing element 12 . In response, the sensing element 12may generate an electrical signal, either a voltage signal or a currentsignal, which may then be processed in order to identify whether theforce is significant and in turn whether the light sensitive screen 10is touched. In one example, the sensing element 12 may be disposed atone of a front surface and a back surface of the light sensitive screen10. In another example, one or more sensing element 12 may be used forthe light sensitive screen 10.

FIG. 2A is a block diagram illustrating a force sensor module 20according to an example of the present invention. Referring to FIG. 2A,the force sensor module 20 may include a pre-amplifier 22, a rectifier24, a trigger 26 and a digitizer 28. The pre-amplifier 22 maybeconfigured to amplify an electrical signal from the sensing element 12.The rectifier 24 may be configured to convert an amplified electricalsignal from the pre-amplifier 22. In one example, the rectifier 24 mayinclude a full-wave rectifier capable of converting analternating-current (AC) signal into a direct-current (DC) signal. Thetrigger 26 in one example may include a rising-edge trigger capable ofdetecting a rising edge of a rectified signal from the rectifier 24.

FIG. 2B is a circuit diagram illustrating a force sensor module 21according to another example of the present invention. Referring to FIG.2B, the force sensor module 21 may be similar to the force sensor module20 described and illustrated with reference to FIG. 2A except that, forexample, a trigger-and-digitizer module 29 replaces the trigger 26 andthe digitizer 28 illustrated in FIG. 2A. The trigger-and-digitizermodule 29 may be configured to convert a rectified signal from therectifier 24 into a digitized signal, which may serve as an output“force sensing result” of the force sensor module 21. The force sensormodule 21 may further include a filter 23 configured to attenuate orreduce an undesired component such as noise in an amplified signal fromthe pre-amplifier 22.

In the present example, the pre-amplifier 22 and filter 23 may eachinclude at least one operating amplifier. Furthermore, thetrigger-and-digitizer module 29 may include a flip-flop including aninput “T” coupled with a logic high signal “High”. The output ports Qand Q of the trigger-and-digitizer may respectively generate a logichigh signal and logic low signal, and vice versa, depending on theoutput of the rectifier 24, i.e., the output of diode D3 or D4.

FIG. 3A is a waveform diagram illustrating exemplary waveforms of aninput force and an amplified electrical signal. Referring to FIG. 3A,the input force applied to a screen from a force source may berepresented by a square-wave shape 30. The input force may be detectedby the sensing element 12, which in turn may generate an electricalsignal. The electrical signal may be an AC signal including a positivefirst half 31 and a negative second half 32. Moreover, the electricalsignal may then be amplified and filtered, resulting in the amplifiedelectrical signal. The waveform of the amplified electrical signal mayinclude the first half 31, which may represent that the input force isexerted on the screen, and the second half 32, which may represent thatthe input force is released from the screen.

FIG. 3B is a waveform diagram illustrating an exemplary waveform of arectified signal from the rectifier module 24 illustrated in FIG. 2B.Referring to FIG. 3B, the amplified electrical signal may be convertedfrom an AC signal into a DC signal by the rectifier 24. For example, thenegative second half 32 may be converted into a positive one 32-1 byrectification.

FIG. 3C is a diagram illustrating exemplary pulses from the trigger 26illustrated in FIG. 2A. Referring to FIG. 3C, the trigger 26 may beconfigured to fetch rising edges of the rectified signal and generatepulse signals 33 and 34 when the rising edges are detected.

FIG. 3D is a waveform diagram illustrating an exemplary waveform of anoutput 35 from the digitizer 28 illustrated in FIG. 2A. Referring toFIG. 3D, the digitizer 28 may latch the pulse signals 33 and 34 andgenerate the output 35 as a force sensing result. The output 35 from thedigitizer 28 may have a square-wave shape and may include an activeperiod spanning between the rising edges.

FIG. 4A is a block diagram illustrating a force sensor module 40according to yet another example of the present invention. Referring toFIG. 4A, the force sensor module 40 may include an integrator 44 and adigitizer 46 in addition to the pre-amplifier 22. The integrator 44 maybe configured to integrate an amplified electrical signal from thepre-amplifier 22 and generate an integrated signal 51 as illustrated inFIG. 5A. Furthermore, the digitizer 46 may be configured to convert theintegrated signal 51 generated by the integrator 44 into a digitizedforce sensing result. Based on the integrated signal 51 from theintegrator 44, the digitizer 46 may generate an output 52 as illustratedin FIG. 5B. Referring to FIG. 5B, the digitizer 46 maybe configured tocompare the integrated signal 51 with a threshold V_(TH). The output 52from the digitizer 46 may have a square-wave shape and may include anactive period from t₁ to t₂, during which the integrated signal 51 has alevel greater than or equal to the threshold V_(TH).

FIG. 4B is a circuit diagram illustrating a force sensor module 41according to still another example of the present invention. Referringto FIG. 4B, the force sensor module 41 may be similar to the forcesensor module 40 described and illustrated with reference to FIG. 4Aexcept that, for example, the force sensor module 41 may further includethe filter 23. In the present example, the pre-amplifier 22, the filter23, the integrator 44 and the digitizer 46 may each include at least oneoperating amplifier.

FIG. 6A is a block diagram illustrating a force sensor module 60according to yet still another example of the present invention.Referring to FIG. 6A, the force sensor module 60 may include a peakdetector 66 and a digitizer 68 in addition to the pre-amplifier 22 andthe rectifier 24 . The peak detector 66 may be configured to detect peaksignal(s) of the rectified signal from the rectifier 24 and feed thedetected peak signal(s) into the digitizer 68, which in turn may convertthe detected peak signal(s) into a digitized force sensing result.

FIG. 6B is a circuit diagram illustrating a force sensor module 61according to yet another example of the present invention. Referring toFIG. 6B, the force sensor module 61 may be similar to the force sensormodule 60 described and illustrated with reference to FIG. 6A exceptthat, for example, the force sensor module 61 may further include thefilter 23. Moreover, in the present example, the peak detector 66 mayinclude at least one operating amplifier.

FIG. 7A is a diagram illustrating exemplary peak signals from the peakdetector 66. Referring to FIG. 7A, peak values of a first half 71 and asecond half 71-1 of a rectified signal from the rectifier 24 may bedetected at time points t₃ and t₄, respectively. Based on the peaksignals at t₃ and t₄, the digitizer 68 may generate an output 72 asillustrated in FIG. 7B. Referring to FIG. 7B, the output 72 from thedigitizer 68 may have a square-wave shape and may include an activeperiod from t₃ to t₄.

FIG. 8A is a block diagram illustrating a force sensor module 80according to still another example of the present invention. Referringto FIG. 8A, the force sensor module 80 may include a comparator 84 inaddition to the pre-amplifier 22 and the filter 23. The comparator 84may be configured to compared a filtered signal from the filter 23 witha threshold. If the filtered signal is greater than or equal to thethreshold, the comparator 84 may generate a force sensing result toindicate that a force applied to the light sensitive screen 10 issignificant and the light sensitive screen 10 is actually touched. Inone example, the electrical signal from the sensing element 12 may beprocessed at the filter 23 prior to the pre-amplifier 22. In anotherexample, the threshold of the comparator 84 may be changeable to suitdifferent applications. In still another example, the comparator 84 maycompare the filtered signal with at least one threshold, and may beconfigured to generate a first force sensing result related to a touchstatus and a second force sensing result related to, for example, themagnitude of a force applied to the light sensitive screen 10.

FIG. 8B is a circuit diagram illustrating a force sensor module 81according to yet another example of the present invention. Referring toFIG. 8B, the force sensor module 81 may be similar to the force sensormodule 80 described and illustrated with reference to FIG. 8A exceptthat, for example, the force sensor module 81 may further include adigitizer 86, which may be configured to convert a force result signalfrom the comparator 84 into a digitized force sensing result. In thepresent example, the comparator 84 may include at least one operatingamplifier, and the digitizer 86 may include an SR latch or SR flip-flopincluding a setting input “S” and a reset input “R”.

FIG. 9A is a waveform diagram illustrating exemplary waveforms of aninput force and an amplified electrical signal, wherein the input forceapplied to a screen from a force source and an electrical signalgenerated by the sensing element 12 may be similar to those describedand illustrated with reference to FIG. 3A.

FIGS. 9B and 9C are waveform diagrams illustrating exemplary waveformsof output voltages of the comparator 84 illustrated in FIG. 8B.Referring to FIGS. 9B and 9C, based on the amplified electrical signal,a pair of output voltages V_(OUT) (FIG. 9B) and V_(OUT) (FIG. 9C) may begenerated by the comparator 84. The pair of output voltages V_(OUT) andV_(OUT) may have substantially the same amplitude but 180 degrees out ofphase with one another. In one example, if the first half 31 has a levelequal to or greater than an upper threshold V_(U), then V_(OUT) for thefirst half 31 is positive while V_(OUT) for the first half is negative,and vice versa. Likewise, if the second half 32 has a level smaller thana lower threshold V_(L), or has a level greater than the lower thresholdV_(L) in absolute value, V_(OUT) for the second half 32 is negativewhile V_(OUT) for the second half 32 is positive, and vice versa. Theupper threshold V_(U) and the lower threshold V_(L) may havesubstantially the same value with different signs.

FIG. 9D is a waveform diagram illustrating an exemplary waveform 90 ofthe force sensing result generated from the digitizer 86 illustrated inFIG. 8B. Referring to FIG. 9D, V_(OUT) and V_(OUT) from the comparator84 are fed to the set “S” and reset “R” inputs of the SR latch of thedigitizer 86, respectively. The digitizer 86 may generate the output 90based on the values of V_(OUT) and V_(OUT) . In the present example, theoutput 90 may have a square-wave shape and may include an active periodspanning from the setting till the reset of the digitizer 86. The activeperiod of the output 90, which may refer to a logic “1” period, mayrepresent a period that the input force is applied to a screen.Accordingly, the force sensor module 81 described and illustrated withreference to FIG. 8B may function like a switch to allow or reject aninput to the screen based on the magnitude of an input force.

It will be appreciated by those skilled in the art that changes could bemade to the examples described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular examples disclosed, but it isintended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

Further, in describing representative examples of the present invention,the specification may have presented the method and/or process of thepresent invention as a particular sequence of steps. However, to theextent that the method or process does not rely on the particular orderof steps set forth herein, the method or process should not be limitedto the particular sequence of steps described. As one of ordinary skillin the art would appreciate, other sequences of steps may be possible .Therefore, the particular order of the steps set forth in thespecification should not be construed as limitations on the claims. Inaddition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A light sensitive screen comprising: at least one sensing elementeach being configured to detect a force applied to a position of thelight sensitive screen and generate an electrical signal when a force isdetected; and a sensor module configured to receive and process theelectrical signal from the at least one sensing element, the sensormodule comprising: an amplifier configured to amplify the electricalsignal from one of the at least one sensing element and generate anamplified signal; a rectifier configured to convert the amplified signalinto a direct-current (DC) signal including a first positive half and asecond positive half; a trigger configured to detect an edge each of thefirst positive half and the second positive half, and generate a firstpulse signal and a second pulse signal for the first positive half andthe second positive half, respectively; and a digitizer configured togenerate a digital signal based on the first pulse signal and the secondpulse signal, the digital signal including information as to whether theposition of the light sensitive screen is touched.
 2. The lightsensitive screen of claim 1, wherein each of the at least one sensingelement includes one of a piezoelectric element or a piezoresistiveelement.
 3. The light sensitive screen of claim 1, wherein the amplifierincludes a pre-amplifier and a filter.
 4. The light sensitive screen ofclaim 1, wherein the digital signal includes an active period from theoccurrence of the first pulse signal to the occurrence of the secondpulse signal.